The intramural Laboratories of Epidemiology, Demography and Biometry (EDB) and Clinical Investigation are supporting a clinical research study, the Dynamics of Health, Aging and Body Composition (HEALTH ABC). This study, targeted to under-standing the decline in function of healthier older persons, complements research efforts in prevention of functional decline for healthy and frail older persons by focusing on the substantial majority of older persons in transition from vigor to frailty. The major objectives of the HEALTH ABC Study relate to observations that change in body composition in old age, particularly the increase in body fat and the decline in lean mass and bone mineral, represent a common pathway by which multiple diseases contribute to disability. There are many unanswered questions regarding the patterns and health impact of changes in weight and body composition in old age. Weight generally increases over the lifetime until late middle age, then tends to decrease into old age with changes in muscle, fat and bone. It has been postulated that the accelerated loss of muscle and strength in old age contributes to the onset of disability. Studies of weight and its relationship to mortality in older persons have yielded contradictory findings, leading to controversy regarding public health recommendations for weight in old age. Few studies have examined weight-related morbidity in old age, especially among African-Americans.